It is based around the idea that some people are being betrayed by their fiercest protector. That their immune system is altering their brain.
The illness exacts a heavy toll on 350 million people around the world, among them Hayley Mason, from Cambridgeshire:
“My depression gets so bad that I can’t leave the bed, I can’t leave the bedroom, I can’t go downstairs and be with my partner and his kids.
The 30-year-old added: “I can’t have the TV on, I can’t have noise and light, I have suicidal thoughts, I have self-harmed, I can’t leave the house, I can’t drive.
“And just generally I am completely confined to my own home and everything else just feels too much.”
Anti-depressant drugs and psychological treatments, like cognitive behavioural therapy, help the majority of people.
But many don’t respond to existing therapies and so some scientists are now exploring a new frontier – whether the immune system could be causing depression.
“I think we have to be quite radical,” says Prof Ed Bullmore, the head of psychiatry at the University of Cambridge.
He’s at the forefront of this new approach: “Recent history is telling us if we want to make therapeutic breakthroughs in an area which remains incredibly important in terms of disability and suffering then we’ve got to think differently.”
The focus is on an errant immune system causing inflammation in the body and altering mood.
And Prof Bullmore argues that’s something we can all relate to, if we just think back to the last time we had a cold or flu.
He said: “Depression and inflammation often go hand in hand, if you have flu, the immune system reacts to that, you become inflamed and very often people find that their mood changes too.
“Their behaviour changes, they may become less sociable, more sleepy, more withdrawn.
“They may begin to have some of the negative ways of thinking that are characteristic of depression and all of that follows an infection.”